2018ApJ...864...24B

The coronal temperature of Capella and Procyon has been derived from the spectral emission of Fe XVII observed in high resolution with Chandra's High Energy Transmission Grating Spectrometer. The measurement makes use of well resolved dielectronic satellite features with a spectator electron in the n = 4 shell. This method does not require a priori knowledge of the ionization equilibrium or of the elemental abundances. We find the temperature of Fe XVII emission is 264_–51⁺¹⁴² eV for Procyon and 514_–25⁺²⁷ eV for Capella, i.e., 3.1 and 6.0 MK, respectively. The Procyon measurement is based on three X-rays observed in the dielectronic satellite feature, which illustrates the power of the method even for low-signal observations.